We study the spin-dependent transport properties of a spin valve based on a double quantum dot. Each quantum dot is assumed to be strongly coupled to its own ferromagnetic lead, while the coupling between the dots is relatively weak. The current flowing through the system is determined within perturbation theory in the hopping between the dots, whereas the spectrum of a quantum-dot–ferromagnetic-lead subsystem is determined by means of the numerical renormalization group method. The spin-dependent charge fluctuations between ferromagnets and quantum dots generate an effective exchange field, which splits the double-dot levels. Such a field can be controlled, separately for each quantum dot, by the gate voltages or by changing the magnetic configuration of the external leads. We demonstrate that the considered double-quantum-dot spin-valve setup exhibits enhanced magnetoresistive properties, including both normal and inverse tunnel magnetoresistance. We also show that this system allows for the generation of highly spin-polarized currents, which can be controlled by purely electrical means. The considered double quantum dot with ferromagnetic contacts can thus serve as an efficient voltage-tunable spin valve characterized by high output parameters.

中文翻译：

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基于双量子点的大电压可调自旋阀

我们研究了基于双量子点的自旋阀的自旋相关传输特性。假设每个量子点与其自身的铁磁引线强耦合，而点之间的耦合相对较弱。流经系统的电流是在点之间跳跃的微扰理论中确定的，而量子点-铁磁-铅子系统的光谱是通过数值重整化群方法确定的。铁磁体和量子点之间与自旋相关的电荷波动会产生有效的交换场，从而分裂双点能级。这样的场可以通过栅极电压或通过改变外部引线的磁性配置来单独控制每个量子点。我们证明了所考虑的双量子点自旋阀装置表现出增强的磁阻特性，包括正常和反向隧道磁阻。我们还表明，该系统允许产生高度自旋极化的电流，可以通过纯电气方式控制。因此，所考虑的具有铁磁接触的双量子点可以用作具有高输出参数的高效电压可调自旋阀。